Process for extracting hydrocyanic acid from gases



M. E. MUELLER.

PROCESS FOR EXTRACTING HYDROCYANIC ACID FROM GASES,

APPLICATION FILED MAR.|0,192.

Patented Apr. 25, 1922.

P/zEc/P/'TA TE. STE P COZ EXPELLED v AWV v A pletely as cuprous sulphide MAX E. MUELLER, OF YOUNGSTOWN, OHIO.

YPIRCR'JESS FORVEXTRACTING HYDROCYANIC ACID FROM GASES.

Specification of Letters Patent. Iatelltd Apr. 25, 1922.

Application filed March 10, 1921. Serial No. 451,215.

To all whom t may concer-ri:

Be it known that I, MAX E. MUELLER, a citizen of the United States, and a 'resident of Youngstown, count-y of Mahoning, and State of Ohio, have'invented a new and useful Improvement in Processes for Extracting Hydrocyanic Acid from Gases, of which the following is a Specification, the principle of the in-vention being' herein explained and the best mode in which I have contemplated applying' that principle,` so as to distinguish itv from other invehtions.

In the extraction or recovery ofhydrocyanic acid from coal gas by means of copper compounds in the presence of ammonia, the solution obtained contains, besides ammonium cupro-cyanide, hydrogen sulphide combined as ammonium sulphide. If the solution thus obtained is distilled with dilute sulphuric acid the copper present in solution is converted either in whole or in part to cuprous sulphide and the cyanogen is liberated either Wholly or in part and distills otf as hydrocyanic acid. In all cases the maximum possible amount of cuprous sulphide will be formed. It there is an excess of hydrogen sulphide over the amount necessary to form cuprous sulphide with all the copper in solution then on distilling the solution with dilute sulphuric acid the copper will be precipitated comand the cyanide completely liberated hydrocyanie acid. The excess ot hydrogen sulphide will also be liberated and will contaminate the hydrocyanic acid. If there is an insufficiency ol` hydrogen sulphide to combine with all the copper' in solution as cuprous sulphide, then on distilling the solution with dilute sulphuric acid the hydrogen. sulphide will be completely precipitatel as cuprous sulphide and none Will be driven otf. In this case the excess of copper over and above that converted to cuprous sulphide will be converted to insoluble cuprous cyanide (CuCN) which is not decomposed? by dilute sulphuric acid. Any excess of cyanide above that required to form cuprous cyanide with the excess of copper over the equivalent amount of hydrogen sulphide will be liberated and distil olf. In order that no hydrogen sul! phide be distilled oit' with the hydrocyanic acid it is therefore necessary that there be Apresent in the solution at least two atoms of copper for each` molecule of hydrogen sulphide. ,j'flhe present improved method or process is' based on the recognition of the fore- ,going conditions, and consists of the steps hereinafter fully described and particularly pointed out in the claims, the annexed drawing and the ting forth in detail one approved method of carrying out fthe invention, such disclosed mode, however, constitutingbut one of the various ways inwliich the principle of the invention may be used.

In said annexed"drasvingiI` The single figure there appearing is a diagrammatic representation of the several steps that enter into the process.

As one illustrative Way in which the distilling off of hydrogen sulphide with the hydrocyanic acid may be avoided, the absorbing' medium which in practice will consist of a suspension of cuproussulphide in water, may be exposed to the action of the for a sufficient length ot. time to arrive at the necessary condition of two atoms ot' copper in solution for one molecule ot' hyrdog'en sulphide. The amount of copper which goes into solution depends on the amount of hydrocyanic acid absorbed from the gas with the formation ot' an ammonium cupio-cyanide ot' the probable composition (Nll)2(u( ,N) This would re` quire the absorption of six molecules of hydrocyanic acid ior every molecule of hydrogen sulphide. As coal gas contains a far higher proportion of hydrogen sulphide than of hydrocyanic acid, the absorption of the former will at first be far in excess oi the ratio oi one molecule of such sulphide to six molecules of the acid. The solution will, however, soon become saturated with the hydrogen sulphide so that if Suthcient is passed through the solution with the resulting absorption of more hydrocyanic acid and solution of copper, a condition will be reached where there are more than two atoms of copper in solution for each molecule'ot` the sulphide. Such a solution on distilling with dilute sulphuric acid will liberate hydrocyanic acid Without any hydrogen sulphide.

y way ot varying the foregoing procefollowing' description seti dure for obtaining the result stated, the s0- lution obtained by scrubbing coal gas with water carrying a copper compound such as cuprous sulphide in suspension, may be heated to drive off a portion of the hydrogen sulphide in order to bring the ratio of the copper to the sulphide in solution to the ratio of at least two atoms of copper to one molecule otl the sulphide. This opera-A tion, however, will usually result in some hydrocyanic acid being driven off withthe sulphide.

'Whichever procedure be followed, in 0rder to insure the presence in the solution ot at least two atoms of vcopper for each molecule of hydrogen sulphide, the solution obtained by scrubbing the coal gas with water carrying in suspension a compound of` copper such as cuprous sulphide will contain in addition to ammonium cupro-cyanide and hydrogen sulphide, varying amounts of carbon dioxide as ammonium carbonate. On distilling this solution with dilute sulphuric acid the carbon dioxide will be liberated and contaminate the h vdrocyanic acid distilled otl'. To overcome this difficulty the solut-ion may be boiled before distilling with Sulphurie acid. whereby the carbon dioxide iS removed. .\t the same time, however, a. considerable amount of the cvanide will be driven ott' as hydrocya-nie acid. The loss of acid on boiling the solution to remove carbon dioxide can be prevented by adding to the solution an excessrotcuprous cyanide. The addition otl cuprous'cyanide to the solution will result first, in precipitating any hydrogen sulphide present. with the formation ot' cupi-ous sulphide and ammonium cupro.

(n (Nirogsafeieaou:

ca ,s+(ivungtmmo,4

On heating` the solution with an excess of cupi-ous cyanide the cuprous c vanide will dissolve, probably with the formation of another ammonium cupro-c-yanide ot thel coniposition, NH4C11(CN) 2 (2) (NH4):Cu(CN)-l-C.\1CN= The solution thus obtained may be boiled and the carbon dioxide driven 01T without appreciable loss of hydrocya-nic acid. Then on distilling with dilute sulphurie acid7 hydrocyanic acid t'rec from both hydrogen sulphide and carbon dioxide will be liberated and there will remain an insoluble residue ot cupi-ous, cyanide.

'lhe cnprous c vanidc produced is added to subsequent batches ol solution obtained by cvanide. as `represented by the following cisnes scrubbing the gas in order to precipitate sulphides and prevent loss of hydrocyanic acid when the solution is boiled to remove carbon dioxide. The hydrocyanic acid lib-v era-ted on distillation with sulphuric acid may be either absorbed in caustic soda or condensed as liquid hydrocyanic acid.

It would seem at first sight. that by use of this method of removing sulphides from thev solution by the addition of ycuprous cyanide the necessity of having two atoms of copper in solution for each molecule of hydrogen sulphide would be. obviated. Such7 however, is not the case. Unless this condition is observed it will be found that there will be an insuliciency of copper cyanide to repeat the cycle of operations over and over again. By observing the condition regard ing the ratio of copper in solution to hydrogen sulphide the cycle of operations is seli sustaining, in so far as-copper compounds are concerned. The various reactions in this caseI may be represented by equations (et), and (6) which follow (Je) y Absorption of HUN, HZS and C02 from gas;

It will be' seenthat when starting with cuprous sulphide no hydrogen sulphide can be absorbed from the gas and maintain the ratio of two atoms of copper to onevmolecule of suchhydrogen sulphide in solution. Any of the latter absorbed in the early stages ot the scrubbing operation must again be liberated in the latter stages.

(5) Treatment of` the solution with CuCN and expelling of'CO2 by boiling z-eA @(NHJQC(CN)3+(NH.)2S+(NHMCM -l-GCuCNzGNHu(CN)2{C112S{2NH, +C0 .+H20. f

(6) Distillationi with dilute sulphuric acid GNILCu CN) 2+2NH3+lHS ica lll@

By equation (-6) the six molecules of hyl droeyanic acid absorbed in equa-tion ("4) are liberated and the six molecules of copper cyanide needed for equation (5) are again produced. Furthermore, the one molecule of copper sulphide required in equation (fr) is recovered by equation (5).

It' the absorption of hydrocyanic acid and the solution of copper sulphide in the scrubber continues beyond the stage where there are two atoms ot' copper in solution for each molecule of hydrogen sulphide. or ii the solution as it comes trom the scrubber is heated and a portion of suclrsnlphide removed so that the above ratio is exceeded. then the c vclc of operations is Still self sustaining in so far as the copper requirements are concerned. Assuming the amount of copper in solution is fifty per cent greater than required to fulfill the condition of two atoms of copper toone molecule of HES, the operations represented by equations (5) and v(6) above, will be represented by equations (7) and (8), which follow rc) MNH.).Cucine@Matsuura2 co3 7ouoN=sNH4ou (cN) 2 ca ,saV 2NH3+co2+H2o andsonori-p5 (NH4) 2SO,+8HCN.

It will be seen that in this case there is more copper cyanide produced by equation (8) than is re ulred for equation (7). This excess of Gu N may be returned to the scrubber with the copper sulphide produced by: the step of equation (7) Vor the excess of copper cyanide may be withdrawn from the system and the copper so withdrawn maybe replaced in some other form, for example, by additional copper sulphide.

I have found that in the operation of this Aprocess some sulphocyanide is produced which appears .in the residue from the distillation with sulphuric acid as cuprous sulphocyanide. This in no way interferes with the process as 'the cuprous sulphocyanide is 'equallycas effective as cuprous cyanide in preventing"'-the loss of hydrocyanic acid when the solution from the absorptlon step of'the process is boiled to expel carbon d1.

Other modes of applying the principle ot my invention may be employed instead of the one explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the ol.

lstep which consists in forming a double copper cyanide with said acid; there being present in the solution at least two atoms of rdvcopper for each molecule of hydrogen sulphide.

2. In a method of recovering hydrocyanic acid fromgases also containing hydrogen sulphide, carbon dioxide and ammonia, thel steps which consists in forming a double copper cyanide with said acid, there belng present in the solution at least two atoms of copper for each molecule of hydrogen s ulphide, and then distilling such solution with acid.

dilute acid capable of liberating hydrocyanic -steps which consist in absorbing said acid by means of a copper compound in the presence of water, whereby a solution of a double ammonium copper cyanide is formed in which at least two atoms of copper are preisent for each 4molecule of hydrogen sulphide, and then distilling such solution with dilute sulphuric acid, whereby'hydrocyanic acid is 75 liberated and the copper present completely precipitated as copper sulphide and cyanide.

4. In a method of recovering hydrocyanic acid from gases also containing hydrogen sulphide, carbon dioxide and ammonia, the steps which consists in absorbing said acid by means of a copper-compound in the presence of water, whereby a solution of a double ammonium copper cyanide is formed in which at least-two atoms of copper are present for each molecule of hydrogen sulphide, and then distilling such solution with dilute sulphuric acid, whereby hydrocyanic acid is liberated and the .copper present completely precipitated as copper sulphide and cyanide, and thenreturning such copper sulphide and cyanide to the lirst step for treating more gas.

5. In a method of recovering hydrocyanic acid fromv gases also containing hydrogen sulphide, carbon dioxide and ammonia, the steps which consist in absorbing said acid by means of a copper compound in the' presence of water, whereby a solution of a double ammonium copper cyanide is formed, adding to such solution an excess of cuprous cyanide, boiling such solution to drive ofi` the carbon dioxide, and then distilling such solution with dilute acid capable of liberating hydrocyanic acid. a 105 6. In a method of recovering hydrocyanic f acid from gases also containing hydrogen sulphide, carbon dioxide and ammonia, the steps which consists in absorbing said acid by means of a copper compound in the pres'- ence of water, whereby a solution of a double ammonium copper cyanide is formed, adding to such solution an excess ot cuprous cyanide, boiling such solution to drive oil' the carbon dioxide, the cuprous cyanide precipitating any hydrogen sulphide present as cuprous sulphide, returning the latter to the first step for treating more gas, and then distillin ysuch solution with dilute acid-capable o liberating hydrocyanic acid.

.7. In a method of recovering hydrocyanic acid from gases also containing hydrogen sulphide, carbon dioxide and ammonia, the

cyanide, boiling,` such Solution to drive off the carbon dioxide, the cuprous cyanide precipituting any hydrogen sulphide present as Cuprous sulphide, returning the latter lo 'mha first step 'for treating; more gas, then distilling such solution with :i dilute acid capable of liberating hydrocyzmic acid, the

- www@ copper kpresent being precipitatedas copper Cyanide, and returning such cyanide to the resulting solution to precipitate furthehyl@ drogen sulphide.

Signed hv me, this 3rd day of March, 1.921.

MAX. MUELLER., 

